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Assignment of mite-transmitted species to the genus Rymovirus (family Potyviridae) has changed several times, and the status of the genus has been questioned. To address this issue, complete genome sequences of the rymoviruses Agropyron mosaic virus (AgMV) and Hordeum mosaic virus (HoMV) were determined. AgMV (9540 nucleotides) and HoMV (9463 nucleotides) each encode a single polyprotein with proteinase cleavage sites demarcating protein products characteristic of monopartite species of the family Potyviridae. Of the described species of Potyviridae, AgMV and HoMV are most closely related to each other (68.5% nucleotide and 71.6% amino acid sequence identity) and equidistant (about 53% nucleotide and about 49% amino acid sequence identity) from a third rymovirus, Ryegrass mosaic virus (RGMV). Phylogenetic analyses by neighbor joining, maximum parsimony, and Bayesian inference each grouped the three Rymovirus species in an exclusive clade distinct from a clade containing 34 species of the genus Potyvirus. Because AgMV, HoMV, and RGMV share a reciprocal monophyletic relationship with species of the genus Potyvirus and are divergent in sequence and type of vector, the genus Rymovirus should be retained as a taxonomic unit within the family Potyviridae.